Galvanomagnetic sensing elements, such as Hall generators and different types of magnetoresistors (MRs), are widely used in automotive and industrial position and speed sensors. They can operate in most environments as they are relatively unaffected by dirt, most chemicals, oils and other lubricants. They can operate up to reasonably high temperatures (150 or 200 degrees C.) depending on the sensing device material.
The majority of these sensors use one, or at most two, sensing elements. Sensors with a single sensing element are the simplest, but also the least accurate. Sensors with two matched sensing elements spaced some distance apart from each other are used in a differential mode, whereby common mode disturbances are rejected. Two element sensors operating in differential mode provide better accuracy than single element sensors. Since they are capable of locating with high accuracy a particular feature of the sensed object, such as a tooth edge or a center of a slot, such differential sensors are often used as incremental (on-off) sensors, e.g., as crankshaft position sensors. The differential sensor, however, cannot maintain the same high accuracy if it is used as a linear sensor, providing a continuous analog output signal proportional to displacement. This is especially true where relatively large displacements, i.e., those on the order of five mm or higher, are measured.